The present invention relates to a three-dimensional interferometric length-measuring device in which the three dimensions of workpieces or test pieces can be determined with a high degree of accuracy.
In particular, in the production of imaging systems for response to radiation of extremely short wavelength, for example, reflectors used in x-ray astronomy, a measuring device is required which will permit three-dimensional measurements of a precision which is up to about two orders of magnitude better than can be achieved with traditional multiple-coordinate measuring machines. A measuring device which is suitable for use for this purpose must incorporate interferometric length-measuring systems, in order to be able to achieve the required resolution, typically 10 nm.
Present interferometric measuring devices which measure in three coordinates are of generally the construction known from multiple-coordinate measuring machines wherein measuring systems are disposed on the guides of the machine. One such measuring device is described in West German Pat. No. 2,109,954. In that case, the position of a work table, which is movable in three directions in space relative to a machining head, is determined by means of a single laser beam which undergoes multiple reflection along the guides of movable components of the device. In this arrangement, there is a considerable violation of the comparative principle with respect to all three measurement axes. Errors in the guides of the measuring device therefore limit the theoretically achievable precision of interferometric measurement. West German Pat. No. 2,159,134, West German Pat. No. 2,164,898 and West German published application No. OS 2,441,984, disclose comparators having interferometric measurement systems in two coordinate directions. However, said patents do not contain any suggestion as to the arrangement of an interferometer system for the additional third coordinate direction.